The present invention relates to cell selection in a mobile telecommunications network and especially to preventing some subscribers from camping in an exclusive access cell.
Mobile communications system generally refers to any telecommunications system which enables wireless communication when users are moving within the service area of the system. A typical mobile communications system is a Public Land Mobile Network (PLMN).
In cellular mobile communications systems, like the pan-European mobile communications system GSM (Global System for Mobile Communications), a mobile station may roam freely within the area of the mobile communications network and switch from one cell to another. Normally a mobile station camps in the cell the base station signal of which is best at the moment. Usually, all base stations provide substantially similar services for the mobile stations in a network. Some base stations can, however, be defined to provide a certain special service for all mobile stations of the network, e.g. call charges below the normal tariff. The base station broadcasts a message on such a special service on its broadcast control channel, whereby mobile stations in the cell served by the base station note that they are within a special service area of the network and may take advantage of this service.
Within the context of this application, such special service areas are referred to as localized service areas LSA and support for LSA is called SoLSA. A subscriber having a SoLSA service is called a SoLSA subscriber. A mobile station currently having support for the SoLSA is said to be in LSA mode. This could mean e.g. that the mobile station indicates to its user that certain special features (like lower rates or extra services) are available, and it uses these features when applicable. However, the mobile stations not supporting the SoLSA are not impacted by the presence of LSA services. The SoLSA for a GSM environment is described in a proposal to the ETSI (European Telecommunication Standard Institute), document GSM 03.73, version 2.0.0 which is incorporated herein by reference, but for convenience, the parts of this document which are essential for understanding the invention are repeated in this application.
The concept of LSA extends the operator's capability to offer different service features to subscribers or subscriber groups, different tariffs and different access rights depending on the location of the subscriber. Examples of LSAs are indoor office cells (those provided by indoor base stations); a home or an office and its neighbourhood, an industry area (covering all company buildings and the space between), or part or several locations of a city.
The network operator can define an LSA consisting of a cell or a number of cells. The cells constituting a LSA may not necessarily provide continuous coverage. It is possible for the network operator to set certain characteristics/attributes to each LSA. Some LSA related attributes may be managed as part of cell management. One cell may belong to one or more LSAs. There may also be cells which do not belong to any LSA. The LSA is identified by an LSA ID. For a subscriber, the network operator may define one or more LSA(s) as allowed LSA(s).
One feature of the concept of LSA is exclusive access EA. The EA attributes may be managed as part of cell management. An exclusive access cell is a cell where only mobile stations having the same exclusive access information as the cell are allowed to camp. With the EA it ought to be possible to guarantee that the members of a user group are the only users of the radio channels (physical resources) within a cell. In order to support exclusive access, other users' mobile stations must be prevented from camping in that cell. However, emergency calls should be allowed for every mobile station in that cell.
A problem with the above described is that there is no solution available to separate cells from the mobile stations not belonging to the user group and to allow emergency calls for all mobile stations in these cells including also mobile stations not supporting the SoLSA.